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My 2003 deville has developed a rough idle. When cold it seems to run fine. after it has reached operating temperature it idles rough. Seems to have a miss. I have recently put new ac delco spark plugs, checked for vacumm leaks, plenum gasket is in order, cleaned the throttle body and replaced the crankshaft position sensors. I replaced the cps's because the car stalled as described by other posts and I thought it may be part of the rough idle issue but it still has the problem.

Car has 150k. It is used in a sedan service and is maintained well.

The only codes that are recurring are c1287 and c1288. I believe these refer to the steering position sensor. I am uncertain of any relationship to the rough idle.

I was thinking the o2 sensors but they seem to be working as they should. I am using a scantool and the voltage and short term fuel trim for all three sensors seem to be doing what they are meant to do.

thanks in advance for your help.

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I use a diagnostic tool called Autotap, with it you could determine real time misfires, do you have the ability to do that?

The reason I say this, is that you could locate the mis and focus on that cylinder. I would pull each coil pack and check the plug connections for corrosion and a good positive connection at each plug.

Logan has a famous statement that he makes, he keeps a coil pack in his trunk... Check your coil packs if the connections are OK

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I use a diagnostic tool called Autotap, with it you could determine real time misfires, do you have the ability to do that?

The reason I say this, is that you could locate the mis and focus on that cylinder. I would pull each coil pack and check the plug connections for corrosion and a good positive connection at each plug.

Logan has a famous statement that he makes, he keeps a coil pack in his trunk... Check your coil packs if the connections are OK

I use a a program called digimoto. It is a USB connection to my laptop. I am not sure it can focus on a specific cyl for misfire. It does show misfire test as a constant monitor. But I am assuming it is just reading data from the vehicle and it would only show as a p30? code.

I did have a history code of misfire on cyl 1 but I am not certain how old it was and it has not returned. I will check the coil packs.

I also recleaned the tb and changed the air filter. the fuel filter was recently changed. It seems to be running better. I will have to drive it for a day or so to see if the problem is gone. preliminary drive seems optimistic.

I also read about cleaning the EGR valve. could that be a potential culprit?

Is there a relearn process or special procedure to perform after changing the crankshaft position sensor?

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I use a diagnostic tool called Autotap, with it you could determine real time misfires, do you have the ability to do that?

The reason I say this, is that you could locate the mis and focus on that cylinder. I would pull each coil pack and check the plug connections for corrosion and a good positive connection at each plug.

Logan has a famous statement that he makes, he keeps a coil pack in his trunk... Check your coil packs if the connections are OK

I use a a program called digimoto. It is a USB connection to my laptop. I am not sure it can focus on a specific cyl for misfire. It does show misfire test as a constant monitor. But I am assuming it is just reading data from the vehicle and it would only show as a p30? code.

I did have a history code of misfire on cyl 1 but I am not certain how old it was and it has not returned. I will check the coil packs.

I also recleaned the tb and changed the air filter. the fuel filter was recently changed. It seems to be running better. I will have to drive it for a day or so to see if the problem is gone. preliminary drive seems optimistic.

I also read about cleaning the EGR valve. could that be a potential culprit?

Is there a relearn process or special procedure to perform after changing the crankshaft position sensor?

Thats cool, I use Autotap and it also connects to my laptop via a USB port. I can call up the misfire history and current misfires by cylinder.

Check your #1 coil connections, and possibly swap in a known good coil pack

Have you disconnected the battery after installing the crank sensor?, disconnect the battery and let the system go through a relearn

You would get an EGR pindle position code if it was EGR related and it would idle very poorly

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I finally got an error... misfire on cyl 5. It was initially p0300 and then changed into p0305. I pulled the coil pack and the posts were corroded. I cleaned them and reinstalled the pack. . Still missing. I guess it is time for a coil cassette. Is there anything else I should do before I purchase.

Also, I am getting p0410 secondary air... My pump is working... Is there a way to test the check valves to see if they are working?

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It sounds like you have done a lot already, if there is anyway for you to swap in a known good coil pack, I would do that, any scrap yards near you?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks for all your help... As was suggested the problem was the coil pack. Cleaning the posts did not help.

For your info.... Some prices.

Dealer $335.000

Rockauto.com $290.00 plus shipping

Local parts store $400.00 (Some items are priced better must not be a regular part for them

AUTO ZONE $200.00 Duralast -- Delphi

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